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    <!-- 格式化上下文是怎么样的  FC -->
    <p>
        It can get <strong>very complicated</strong> once you start looking into it.
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    <pre>
    1. html 创建 body 参与共建 第一个BFC
    2. p block container 对内讲产生一个IFC
        由于一行没办法完全显示，所有产生三个线盒(line box) 
        line-height决定高度  
    3. It can get 产生匿名的inline box
    4. very complicated  strong标签产生的inline box
    5. once you 
    6. start looking into it 匿名的inline box
    </pre>
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